Pemphigus vulgaris (PV) is a life-threatening blistering skin disease in which autoantibodies against the cell surface of keratinocytes cause them to separate. Autoantibodies from these patients identify PVA or Dsg3 which is a desmosomal molecule in the desmoglein subfamily of the cadherin supergene family. The original cadherins have been shown to be calcium-dependent cell adhesion molecules. The hypothesis of this proposal is that PVA, like classical cadherins, functions in adhesion and that autoantibodies cause loss of function. Therefore, the general goal of this proposal is to determine the function of PVA and how PV autoantibodies cause disease. The first specific aim is to determine if the extracellular (EC) domain of PVA can mediate homophilic adhesion by examining aggregation of transfected fibroblasts or by producing the EC domain with baculovirus and examining directly its function outside of cells. The second specific aim is to study the functions of the intracellular (IC) subdomains of PVA to determine which regions: bind plakoglobin, confer adhesive function on the EC domain, and direct PVA to the desmosome. The third specific aim is to examine function of PVA in normal tissues by establishing mice genetically deficient in PVA by targeted disruption of the gene with homologous recombination. Examining these mice for phenotypic abnormalities is an in vivo approach for studying possible roles of PVA in normal tissue development, structure, and function. Finally, specific aim four is to establish animal models of PV to determine which subdomains of PVA are involved in disease activity. The studies addressing this aim will also result in valuable anti-Dsg3 reagents. Overall, the applicants expect that this proposal will advance our knowledge not only of tissue specific autoimmune disease but also of the normal mechanisms of epithelial cell adhesion.